Detection of various analytes can be achieved using assays wherein a sample to be tested is contacted with a substrate which reacts in a detectable manner with the analyte.
Immunoassays are a well known method of analysis based on antibody-antigen interactions which allow for an analyte, which usually acts as the antigen, to be detected. Immunoassays are frequently used in fields such as clinical medicine, forensic medicine, environmental testing, food quality assurance, and drug testing to detect a wide range of immunoreactive analytes in test samples. An example of a common immunoassay is a pregnancy test which uses the binding between an antibody and the hormone human chorionic gonadotropin (hCG) in the blood to indicate pregnancy.
Various different immunoassay methodologies are known such as competitive and non-competitive assays. Although different immunoassay methodologies use different ways to distinguish the presence of an analyte, all immunoassays require the use of a labelled substance to identify the presence of the analyte. The labels are usually identifiable by colour and often comprise dyed latex or a metal particle. Alternatively, the label can include a radioactive compound that is detected through is radioactivity.
Conventional assays are successful but it would advantageous to provide a method of indicating the presence of an analyte without the need for coloured or radioactive labels.
Many conventional assay systems have a safety mechanism which involves, in addition to the process detecting the presence of the analyte, a second parallel process that provides a control so that the user can ensure that the assay has been completed successfully. Having such a safety feature is clearly desirable but results in the use of significantly more reagent than is needed for the actual detection and requires a bulkier construction. It would desirable to provide the control without undertaking a parallel process.